The Food-Energy-Water-Waste Nexus (FEWWN) represents the interconnections between food, energy, water, and waste production systems, and it has become a key research area. Enormous quantities of agricultural and organic wastes are produced throughout the FEWWN. Often, these wastes are not treated appropriately because their true costs are rarely quantified, and usually externalized to the environment. This shortcoming is addressed from a systems perspective fused with approaches from ecological economics. A regional bioenergy production model where bioenergy may be produced from ethanol and/or agricultural wastes is constructed. Ecosystem service valuation methods are integrated into the framework, allowing for bioenergy production systems to be designed to minimize ecological damage and/or maximize ecological restoration. These values are captured within a Green Gross Domestic Product (Green GDP) objective that values both energy produced and ecosystem service values lost/gained. System profit is another objective in the multi-objective model. The framework is applied to a bioenergy production system for the U.S. state of New York, which aims to produce 10% more bioenergy compared to its current levels. Net changes in Green GDP ranged from -$16.5 M/y to $90.6 M/y, and corresponding profits ranged from $7.2 M/y to -$74.5 M/y. Corn grain ethanol was the dominant source of bioenergy in solutions with higher profits, while ethanol from corn stover and bioelectricity generated from animal manure biogas contributed more bioenergy in solutions with increasing Green GDP. Results show that there is a trade-off between promoting natural capital/ecological health and financial profit. FEWWN system design should consider these trade-offs moving forward.

Residual resources in agriculture provide prime raw material for bioenergy production whose optimization has potential to promote agricultural economy while mitigating environmental side-effects. Food, energy, water, and land resources are intertwined in agricultural systems. Effective management of bioenergy production, considering the nexus of these resources, is needed for the sustainable development of agriculture, which is challenging because of the uncertainties involved therein. This study proposes an optimization-assessment approach (input/output relationship) for sustainable bioenergy production in agricultural systems. The approach is capable of (1) providing decision makers with the ability to determine optimal policy options among water, land, energy, and livestock, considering the tradeoff between economic and environmental impacts for bioenergy production; (2) helping decision makers identify the level of sustainability of agricultural systems and where the effort should be made for various regions; and (3) dealing with the uncertainties to provide decision alternatives. The proposed approach is applied to a case study in the particular context of northeast China, which is predominantly an agricultural region with large bioenergy potential. The changing range of bioenergy production potential, system costs, and environmental impacts were obtained, based on different schemes for the allocation of agricultural resources among different regions. Economic-environmental impact and sensitivity analyses were conducted, and agricultural system sustainability was assessed in a changing environment. Considering the complexity due to uncertainty, the proposed approach can help manage bioenergy production in agricultural systems in a sustainable way, and will be applicable for similar agriculture-centered regions.

Legacy phosphorus (P) that has accumulated in soils from past inputs of fertilizers and manures is a large secondary global source of P that could substitute manufactured fertilizers, help preserve critical reserves of finite phosphate rock to ensure future food and bioenergy supply, and gradually improve water quality. We explore the issues and management options to better utilize legacy soil P and conclude that it represents a valuable and largely accessible P resource. The future value and period over which legacy soil P can be accessed depends on the amount present and its distribution, its availability to crops and rates of drawdown determined by the cropping system. Full exploitation of legacy P requires a transition to a more holistic system approach to nutrient management based on technological advances in precision farming, plant breeding and microbial engineering together with a greater reliance on recovered and recycled P. We propose the term ‘agro-engineering’ to encompass this integrated approach. Smaller targeted applications of fertilizer P may still be needed to optimize crop yields where legacy soil P cannot fully meet crop demands. Farm profitability margins, the need to recycle animal manures and the extent of local eutrophication problems will dictate when, where and how quickly legacy P is best exploited. Based on our analysis, we outline the stages and drivers in a transition to the full utilization of legacy soil P as part of more sustainable regional and global nutrient management.